1. Field of the Invention
This invention relates to polymerization of vinylpyrrolidone (VP) to form polyvinylpyrrolidone (PVP), and, more particularly, to a process for making PVP having both a predetermined high molecular weight (Mw) (K-90, Mw=650,000) and a low molecular weight distribution (MWD=Mw/Mn=5 or less), and, most preferably, a low residual VP level of &lt;0.1%.
2. Description of the Prior Art
Polymerization of vinylpyrrolidone (VP) by free radical mechanisms to form polyvinylpyrrolidone (PVP) is well known and described in U.S. Pat. Nos. 3,862,915; 4,053,693; 4,058,655; and 4,554,312. In the latter patent, Barabas and Cho disclosed a process for making PVP by polymerizing VP in the presence of t-butylperoxypivalate as a free radical initiator. The solvent employed was water, a mixture of water and isopropyl alcohol, or sec. butyl alcohol, or both. In water alone (Example 1) the PVP product had a K-value of 91.1; however, the MWD, or molecular weight distribution of the PVP product made in water is very high, i.e. about 7, which adversely affects its viscosity and other properties. In a mixture of water and 8.7% isopropanol, (Example 2) the K-value of PVP was only 63.1, corresponding to a low Mw of about 400,000 although the MWD decreased to about 5. A 50% isopropanol-50% water solvent mixture (Example 3) gave a low K-value of 41.8. Similarly, in isopropanol solvent alone, the K-value was 30.5 (Example 4), or 12.2 (Example 5). Accordingly, none of these process conditions provided a PVP product having a K-value of 90 corresponding to a Mw of 650,000 and a MWD of 5 or less, and, most preferably, a low residual VP level of &lt;0.1%.
Accordingly, an object of this invention is to provide a process for preparing PVP having a K-value of 90 corresponding to a Mw of about 650,000, and a MWD of 5 or less, wherein the polymer has polymer chains therein which have more nearly about the same length, and, most preferably, in the form of a solution or powder with a residual vinylpyrrolidone level of &lt;0.1%.
These and other objects and features of the invention will be made apparent from the following description of the invention.